1. Field of the Invention
This invention relates to diffusion of fluids so as to provide laminar flow. More specifically, the invention relates to a device and method for diffusing gases which are flowing into a vacuum chamber so as to create laminar flow and thereby eliminate turbulence inside the chamber.
2. Description of the Prior Art
In semiconductor fabrication, exposure of masks or chip substrates, hereinafter workpieces, to electron and/or ion beams is typically done in a vacuum chamber. However, to move workpieces in and out of the chamber, the vacuum must be broken, thereby bringing the chamber back to atmospheric pressure. Allowing a large quantity of atmospheric pressure gas to quickly flow into the vacuum chamber is desirable in order to decrease fabrication time, thereby decreasing cost.
However, the rapid ingress of gas into the vacuum chamber also causes turbulence therein. Frequently, despite contamination control procedures, a few microscopic dust particles are still present in the chamber. Hence, such turbulence stirs up these dust particles.
Because of the small feature sizes and the thinness of deposited layers, semiconductor devices are particularly vulnerable to contaminants such as dust particles. Specifically, if dust particles settle on the workpiece, the electrical characteristics of the device may be dramatically changed resulting in reduced performance and reliability.
To eliminate the problem of turbulence, the prior art provided a diffuser device at the entranceway of the chamber. Typically, the diffuser device was a sintered diffuser, i.e. a mesh-like body forming a porous structure, which allowed the in-flowing gas to flow through the mesh and thus diffused the gas into a laminar flow. The laminar flow of the gas into the chamber reduced the probability that dust particles would contaminate the workpiece.
However, these sintered-type diffusers have significant numbers of "dead" spaces because of their porous nature. These dead spaces, i.e. the spaces between the mesh, are virtually impossible to clean properly both during fabrication of the diffuser and during its use. Moreover, these dead spaces tend to trap gas, thereby making it very difficult to achieve a hard vacuum which is desirable of semiconductor fabrication.
Also known in the prior art are multiple orifice-type diffusers which merely serve to reduce gas velocity. These diffusers are very difficult to clean because of the large number of orifices which tend to trap dust particles. Furthermore, these orifice-type diffusers must be quite large in order to provide an appropriate flow rate, thereby reducing valuable utility space in the chamber.
Therefore, there is a need for a diffuser in vacuum systems, or other systems, which provides the needed diffusion of gas and also is simple to clean, both during fabrication and after use inside the vacuum chamber.